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Polar Coordinates

Polar Coordinates

Imagine that you and a friend are making your way toward a coffee shop in the middle of a large city. Looking at a map, your friend says that you are about \(1\) mile (\(1.61 km\)) southwest of the coffee shop. You take a look at the same map and see that you are \(4\) blocks across and \(4\) blocks down from the coffee shop.

Polar Coordinates diagram of the coffe shop displaying the directions in terms of horizontal and vertical blocks and in terms of diagonal distance StudySmarterFigure 1. Diagram of the coffee shop's location

In this scenario, you and your friend are both communicating the same information about where you are with respect to the coffee shop. The difference is that, while you used a rectangular coordinate system or Cartesian coordinates, your friend used a polar coordinate system. This article will introduce polar coordinates, how to graph polar coordinates, how to convert between polar and rectangular coordinates, and generalizations of polar coordinates in three dimensions.

Polar Coordinate System

You are probably used to talking about points in the plane by referring to their \(x\) and \(y\) coordinates. This system of labeling points is called the rectangular coordinate system, also known as Cartesian coordinates.

Polar Coordinates a point on the rectangular coordinate system displaying the x coordinate as a horizontal line and the y coordinate as a vertical line StudySmarterFigure 2. The rectangular coordinate system

Polar coordinates are just a different way of labeling points in the plane. Instead of using \(x\) and \(y\) coordinates, the polar coordinate system labels points by how far they are from the origin, \(r\), and their angle \(\theta\) with respect to the positive \(x\)-axis, measured counterclockwise. This angle \(\theta\) is typically measured in radians.

Further below in this article, you can learn how to convert between degrees and radians, just in case you forgot!

Polar Coordinates a point in the polar coordinate system displaying the distance from the origin and the angle made with the positive x-axis StudySmarterFigure 3. The polar coordinate system

In principle, both the angle \(\theta\) and the radial distance \(r\) can take on any real value. In practice, \(r\) values are expressed using only non-negative values, that is

\[ r \in [0,\infty).\]

If \(r\) is zero, then, regardless of \(\theta\), the point \((r,\theta)\) is at the pole.

Polar Coordinates the origin also known as pole StudySmarterFigure 4. The origin, or pole, in polar coordinates

The usual convention is to express it as if \(\theta=0\) to avoid any ambiguity.

As mentioned before, \(r\) can take on negative values, but this is usually not expressed like this. Instead of writing a point \((-r,\theta)\) with a negative \(r\) coordinate, you write the reflection of the point \((r,\theta)\) by adding \(\pi\) to the angle.

Polar Coordinates two points with the same r but with a difference of pi in the angle  StudySmarterFigure 5. A point and its reflection in polar coordinates

The angular coordinate, \(\theta\), is typically expressed using values between \(0\) and \(2\pi\), that is

\[ \theta \in [0,2\pi).\]

Just like the radial coordinate, it is also possible to get a point \((r,-\theta)\) with a negative \(\theta\) coordinate. You can obtain this point by rotating clockwise from the positive x-axis by \(\theta\) instead of counterclockwise.

Polar Coordinates two points with the same r but with opposite theta signs  StudySmarterFigure 6. Two points with opposite \(\theta\) signs

Polar and Cartesian coordinates implicitly introduce the notion of different metrics and different ways of talking about distance. Going back to our coffee shop scenario, you could either say that you and your friend are \(8\) blocks away from the coffee shop (4 blocks across and \(4\) blocks down), or you are \(1\) mile (\(1.61 km\)) away from the coffee shop. Both notions of distance have their advantages. The 'block distance,' called the taxicab metric, tells you how much you need to walk to get to the coffee shop if you must stay on the sidewalk. The 'diagonal distance,' or Euclidean metric, tells you the shortest path you could possibly take to get to the coffee shop, assuming you can cut diagonally across city blocks.

Metrics and their associated metric spaces become increasingly important as you continue to study math and have incredible practical applications in areas ranging from data science to signal processing to quantum mechanics.

Polar Coordinate Terminology

There are several terms that are important to know when working with polar coordinates. The point we call the origin when working with rectangular coordinates is called the pole when working with polar coordinates. What we call the x-axis when working with rectangular coordinates is called the polar axis when working with polar coordinates.

The polar axis is also known as the reference direction.

The distance from the origin denoted as the \(r\) coordinate, is also referred to as the radius, radial coordinate, or radial distance. The \(\theta\) coordinate is called the angular coordinate, polar angle, or azimuth.

Table 1. Terminology used in polar coordinates

Name(s) in Rectangular CoordinatesName(s) in Polar Coordinates
OriginPole
Horizontal axis, or \(x\)-axisPolar axis, or reference direction
Distance from the originRadial coordinate, radius, or radial distance
Counterclockwise angle from the positive \(x\)-axisAngular coordinate, polar angle, or azimuth

Degrees and Radians

The angular coordinate \(\theta\) is generally specified in either degrees or radians. Degrees and radians are just different ways of measuring angles.

Algebraically, the relationship between degrees and radians is as follows:

\[\begin{align} k\pi\text{ radians } &= 180k \text{ degrees } \\ k\text{ degrees } &= \dfrac{k\pi}{180} \text{ radians }\end{align}\]

The angle \(30^{\circ}\) can be written in terms of radians. Using the conversion

\[k\text{ degrees } = \dfrac{k\pi}{180}\text{ radians}, \]

you will get that

\[ \begin{align} 30\text{ degrees } &= \dfrac{30\pi}{180}\text{ radians } \\ &= \dfrac{\pi}{6}\text{ radians}. \end{align}\]

Conversely, an angle of \(\tfrac{\pi}{4}\) radians can be written as degrees. Using the conversion

\[k\pi\text{ radians } = 180k \text{ degrees}, \]

you will get that

\[\begin{align} \frac{\pi}{4}\text{ radians } &= \frac{1 \, \pi \text{ radians}}{4} \\ &= \dfrac{180\text{ degrees}}{4} \\ &= 45 \text{ degrees}. \end{align}\]

Multiple Representations of Points in Polar Coordinates

One of the interesting aspects of working with polar coordinates is that every point has infinitely many polar coordinates that describe it. You noted this earlier for the pole, which we said is represented by \((0,\theta)\) for any value of \(\theta\). For example, the coordinates \((0,0)\), \((0,-\pi)\), and \(\left(0,\tfrac{\sqrt{\pi}}{17}\right)\) all represent the pole.

It is worth noting that this multivalued representation is usually avoided and the coordinates are shown in the range

\[ r \in [0,\infty)\]

and

\[ \theta \in [0,2\pi).\]

However, for some special scenarios, like the description of motion in Physics, these domains are extended so both include all real numbers.

In general, the points \((r,\theta)\) and \((r,\theta+2n\pi)\) for any integer \(n\) describe the same point. The points \((-r,\theta)\) and \((r,\theta+m\pi)\), where \(m\) is an odd integer, also describe the same point.

Geometrically, \((r,\theta)\) and \((r,\theta+2n\pi)\) represent the same point because adding \(2n\pi\) corresponds to rotating the point by \(2n\pi\) radians, or some multiple of 360 degrees. Rotating by a multiple of \(2\pi\) effectively does not change the position of the point, so \((r,\theta)\) and \((r,\theta+2n\pi)\) represent the same point.

Polar Coordinates the same point can be written with the same r and with theta increased by multiples of 2pi  StudySmarterFigure 7. Multiple representations of the same point in polar coordinates

The coordinates \(\left(1,\tfrac{\pi}{4}\right)\) and \(\left(1,\tfrac{9\pi}{4}\right)\) describe the same point since

\[ \begin{align} \frac{9\pi}{4} &=\frac{\pi}{4}+\frac{8\pi}{4}\\ &=\frac{\pi}{4}+2\pi. \end{align}\]

Likewise, the coordinates \(\left(-10,\tfrac{5\pi}{6}\right)\) and \(\left(10,\tfrac{11\pi}{6}\right)\) describe the same point, since

\[\begin{align} \frac{11\pi}{6} &= \frac{5\pi}{6}+\frac{6\pi}{6} \\ &=\frac{5\pi}{6}+\pi. \end{align}\]

How to Convert From Rectangular to Polar Coordinates

By this point, you may already notice that working with polar coordinates has its advantages, so here you can learn how to convert from rectangular coordinates to polar coordinates.

Given a point in Cartesian coordinates, you can find an expression for that same point in polar coordinates. To do so, you can use the formulas

\[\begin{align}r&=\sqrt{x^2+y^2} \\ \theta &= \arctan{\left( \frac{y}{x}\right)}. \end{align} \]

You can also find the arctangent function written as the inverse tangent function, that is

\[ \theta = \tan^{-1}{\left( \frac{y}{x}\right)}.\]

To see where these formulas come from, say you are given a point \((x,y)\) in rectangular coordinates and you want to know its corresponding polar coordinates \((r,\theta)\). If you were to graph the point, you would get something like the following image.

Polar Coordinates a point on the cartesian plane displaying both its rectangular coordinates and its polar coordinates  StudySmarterFigure 8. A point on the plane represented in polar and rectangular coordinates

You can use known facts about right triangles to write the relationships between \(x\), \(y\), \(r\), and \(\theta\). First, notice that you can use the Pythagorean Theorem to write

\[x^2+y^2=r^2.\]

From here, you can solve for \(r\) to obtain the first formula,

\[ r = \sqrt{x^2+y^2}.\]

You can also use the fact that the tangent of an angle \(\theta\) in a right triangle is the ratio of its opposite side to its adjacent side so that you can write

\[ \tan{\theta} = \frac{y}{x}.\]

You can now use the inverse tangent function to isolate \(\theta\), that is

\[ \theta = \arctan{\left( \frac{y}{x}\right)}.\]

The point

\[ P=(3, 4)\]

is given in cartesian coordinates. Write \(P\) in polar coordinates.

Solution:

To find \(r\) you just need to square each component of the point, add them together, and take the square root, that is

\[ \begin{align} r &= \sqrt{x^2+y^2} \\ &= \sqrt{3^2+4^2} \\ &= \sqrt{ 9 +16} \\ &= \sqrt{25} \\ &= 5. \end{align}.\]

Next, find the angle by using

\[\theta = \arctan{\left(\frac{y}{x}\right)}\]

with the help of a calculator, that is

\[ \begin{align} \theta &= \arctan{\frac{y}{x}} \\ &= \arctan{\left(\frac{4}{3} \right)} \\ &= 0.9272. \end{align} \]

Remember that this angle is typically given in radians, so make sure your calculator uses these!

This means that the point \(P\) in polar coordinates is

\[ P =(5,0.9272).\]

Since you need to use the inverse tangent function to find the angle \(\theta\), it is better to discuss this a bit further.

Tangent and Arctangent

When using the formula

\[\theta=\arctan{\left(\frac{y}{x}\right)},\]

you have to be aware of certain technicalities related to the tangent and arctangent functions.

First, notice that this expression is undefined when \(x=0\). In this case, the point \((x,y)\) must lie on the \(y\)-axis. So, \(\theta\) must either be \(\tfrac{\pi}{2}\) or \(-\tfrac{\pi}{2}\), depending on whether \(y\) is positive or negative.

Polar Coordinates two points on the y-axis showing their angle the one in the positive y axis has an angle of pi/2 and the one in the negative y-axis has an angle of -pi/2  StudySmarterFigure 9. Two points in polar coordinates when \(x=0\)

Next, given any \(\tfrac{y}{x}\), there are actually two values of \(\theta\) in \([-\pi,\pi]\) satisfying \(\tan(\theta)=\tfrac{y}{x}\).

Given \(y=1\) and \(x=1\), both the angles \(\tfrac{\pi}{4}\) and \(-\tfrac{3\pi}{4}\) satisfy that

\[ \begin{align} \tan\left(\dfrac{\pi}{4}\right) &=\tan\left(-\dfrac{3\pi}{4}\right) \\ &=\dfrac{y}{x} \\ &=\dfrac{1}{1} \\&=1. \end{align}\]

Notice that these angles are reflections of each other; this is always the case.

To make sure that you are specifying the correct point when writing a point in polar coordinates, you must make sure that the angle \(\theta\) you use is in the correct quadrant. The arctangent function only returns angles between \(-\tfrac{\pi}{2}\) and \(\tfrac{\pi}{2}\), so \(\arctan\left(\tfrac{y}{x}\right)\) only returns the correct value for \(\theta\) if the point \((x,y)\) is in the first or fourth quadrant.

Polar Coordinates graph of the arctangent function along with two horizontal asymptotes at y=pi/2 and y=-pi/2 StudySmarterFigure 10. Graph of the arctangent function

Furthermore, since \(\theta\) values are typically given between \(0\) and \(2\pi\), you also need to do a correction if the angle you obtain from the calculator is negative. The following table summarizes how to find \(\theta\).

Table 2. Relation between the sign of \(x\) and the angle \(\theta\)

QuadrantSign of \(x\)Sign of \(y\)\( \theta\)
I\(+\)\(+\)\(\theta=\arctan\left(\dfrac{y}{x}\right)\)
II\(-\)\(+\)\(\theta=\arctan\left(\dfrac{y}{x}\right)+\pi\)
III\(-\)\(-\)\(\theta=\arctan\left(\dfrac{y}{x}\right)+\pi\)
IV\(+\)\(-\)\(\theta=\arctan\left(\dfrac{y}{x}\right)+2\pi\)

Consider the point \( P= (-2,1) \).

  1. In which quadrant is \(P\)?
  2. Find its \(r\) coordinate.
  3. Find its \(\theta\) coordinate.

Solution:

  1. Since the \(x\)-coordinate is negative and its \(y\)-coordinate is positive, the point \(P\) lies in the second quadrant (II).
  2. This step is rather straightforward, just use the formula for \(r\), that is\[ \begin{align} r &= \sqrt{x^2+y^2} \\ &= \sqrt{(-2)^2+1^2} \\&= \sqrt{4+1} \\&= \sqrt{5}.\end{align} \]
  3. You just found that \(P\) is on the second quadrant, so use a calculator and find that\[\begin{align} \theta &= \arctan{\left( \frac{1}{-2}\right)}+\pi \\ &= \arctan{\left(-0.5\right)}+\pi \\ &= -0.463647+3.141592 \\ &= 2.677945.\end{align}\]

How to Convert From Polar to Rectangular Coordinates

Now suppose you are given a point in polar coordinates and you want to know how to express this point using rectangular coordinates. For this case, you can also use the same diagram of the right triangle that relates \(x\), \(y\), \(r\), and \(\theta\).

Polar Coordinates a point on the cartesian plane displaying both its rectangular coordinates and its polar coordinates  StudySmarterFigure 11. A point on the plane represented in polar and rectangular coordinates

Focus on the angle \(\theta\). Since you have a right triangle, you can write the sine of the angle as:

\[ \sin{\theta} = \frac{y}{r}\]

Likewise, the cosine of the angle is:

\[ \cos{\theta} = \frac{x}{r}\]

Solving each expression for \(x\) and \(y\) will yield you:

\[ x=r\,\cos{\theta}\]

and

\[ y=r\,\sin{\theta}\]

Unlike when passing from rectangular coordinates to polar coordinates, the above expressions do not need you to watch out for any special considerations. These are as straightforward as it gets!

You previously found that the point \(P=(-2,1) \) had:

\[ r = \sqrt{5}\]

and

\[ \theta = 2.677945 \]

Verify that the above values are correct.

Solution:

To find the \(x\)-coordinate use:

\[ x = r \, \cos{\theta},\]

so use a calculator and find:

\[ \begin{align} x &= \sqrt{5} \cdot \cos{2.677945} \\ &= -2. \end{align}\]

For the \(y\)-coordinate, use instead:\[ y = r\, \sin{\theta}\]

that is

\[ \begin{align} y &= \sqrt{5} \cdot \sin{2.677945} \\ &= 1. \end{align}\]

The above values are precisely the rectangular coordinates of the point \(P\).

Polar Coordinate Graphers

You can use several electronic resources to graph points in polar coordinates. For example, in Geogebra, you can graph a point \((r,\theta)\) by typing \((r;\theta)\). Many graphing calculators also allow you to plot points using polar coordinates, as do programs and programming languages like Python, Octave, and Matlab. For information on how to graph polar curves, see the article Polar Curves.

Examples of Conversion Between Polar Coordinates and Rectangular Coordinates

Here you can look at some examples of conversion between both coordinate systems!

Examples of Converting from Rectangular to Polar Coordinates

For these examples, suppose you are given a point in rectangular coordinates and you want to find it written in polar coordinates.

Convert the point \[ P= \left(-2\sqrt{3},-2\right)\]

from rectangular to polar coordinates.

Solution:

First, note that this point is in the third quadrant since both \(x\) and \(y\) are negative.

Next, find \(r\) using

\[r=\sqrt{x^2+y^2},\]

that is

\[\begin{align}r&=\sqrt{\left(-2\sqrt{3}\right)^2+(-2)^2} \\ &=\sqrt{4(3)+4} \\ &= \sqrt{12+4} \\ &= \sqrt{16}\\ &=4.\end{align}\]

Next, find theta. Since the point is on the third quadrant you will need to use\[\theta=\arctan\left(\frac{y}{x}\right)+\pi,\]

that is

\[\begin{align}\theta&=\arctan\left(\frac{-2}{-2\sqrt{3}}\right)+\pi \\ &=\arctan\left(\dfrac{1}{\sqrt{3}}\right)+\pi \\ &=\dfrac{\pi}{6}+\pi \\ &=\dfrac{7\pi}{6}.\end{align}\]

Thus, the point \(\left(-2\sqrt{3},-2\right)\) in polar coordinates is \(\left(4,\tfrac{7\pi}{6}\right)\).

Here is another example.

Convert the point

\[ Q = \left(\tfrac{3\sqrt{2}}{2},-\tfrac{3\sqrt{2}}{2}\right)\]

from rectangular to polar coordinates.

Solution:

Begin by noting that this point is in the fourth quadrant because \(x\) is positive and \(y\) is negative.

Now find \(r\) as usual, that is

\[\begin{align} r &= \sqrt{\left(\dfrac{3\sqrt{2}}{2}\right)^2+\left(-\dfrac{3\sqrt{2}}{2}\right)^2} \\ &= \sqrt{\dfrac{9\cdot2}{4}+\dfrac{9\cdot2}{4}} \\ &=\sqrt{\dfrac{9}{2}+\dfrac{9}{2}}\\ &=\sqrt{9} \\ &=3.\end{align}\]

You previously found that the point is on the fourth quadrant, so you will need to use

\[ \theta = \arctan{\left( \frac{y}{x} \right)}+2\pi.\]

Before proceeding, note that the \(x\) and \(y\) values are the same, just with opposite signs. This means that

\[ \frac{y}{x}=-1,\]

so you do not need to write the whole huge fraction, as it will simplify to \(-1\). Knowing this,

\[ \begin{align} \theta &= \arctan{-1}+2\pi \\ &= -\frac{\pi}{4}+2\pi \\ &= \frac{7\pi}{4}.\end{align}\]

This means that the point \(Q\) written in polar coordinates is

\[ Q = \left(3, \frac{7\pi}{4}\right).\]

Examples of Converting from Polar to Rectangular Coordinates

For the next example, suppose you are given a point in polar coordinates and you wish to know how it's written in rectangular coordinates.

Convert the point

\[\left(4,-\tfrac{\pi}{3}\right)\]

from polar to rectangular coordinates.

Solution:

Start by finding \(x\) using the formula \(x=r\cos(\theta)\).

\[\begin{align} x&=4\cos\left(-\dfrac{\pi}{3}\right) \\ &= 4\left(\dfrac{1}{2}\right) \\ &=2.\end{align}\]

Next, find \(y\), using the formula \(y=r\sin(\theta)\).

\[\begin{align} y&=4\sin\left(-\dfrac{\pi}{3}\right) \\ &= 4\left(-\dfrac{\sqrt{3}}{2}\right) \\ &=-2\sqrt{3}.\end{align}\]

So, the point \(\left(4,-\tfrac{\pi}{3}\right)\) in Cartesian coordinates is \((2,-2\sqrt{3})\).

Here comes one last example.

Convert the point

\[\left(5,\tfrac{3\pi}{4}\right)\]

from polar to rectangular coordinates.

Solution:

First, find \(x\) using the formula \(x=r\cos(\theta)\).

\[\begin{align} x&=5\cos\left(\dfrac{3\pi}{4}\right) \\ &= 5\left(-\dfrac{\sqrt{2}}{2}\right) \\ &=-\dfrac{5\sqrt{2}}{2}.\end{align}\]

Then, find \(y\), using the formula \(y=r\sin(\theta)\).

\[\begin{align} x&=5\sin\left(\dfrac{3\pi}{4}\right) \\ &= 5\left(\dfrac{\sqrt{2}}{2}\right) \\ &=\dfrac{5\sqrt{2}}{2}.\end{align}\]

Therefore, the point \(\left(5,\tfrac{3\pi}{4}\right)\) in Cartesian coordinates is \(\left(-\tfrac{5\sqrt{2}}{2},\tfrac{5\sqrt{2}}{2}\right)\).

Don't worry if your calculator is not giving you the exact values of the trigonometric functions. If you give a decimal value the answer is still the same.

Polar Coordinates – Key takeaways

  • The polar coordinate system is a system of labeling points in the plane by their distance from the origin and their angle with respect to the positive x-axis.
  • There are multiple ways to represent any given point in polar coordinates.
  • When converting from rectangular to polar coordinates, be careful about which quadrant your point is in, and be sure to use the appropriate arctangent function.

Frequently Asked Questions about Polar Coordinates

Is a different coordinate system, where you consider the distance between the point and the origin, and the angle between the positive x-axis and the ray that goes from the origin to the point.

You first mark the angle, considering that a positive angle is measured counterclockwise, and a negative angle is measured clockwise. Then you trace the given distance for r in the direction of the angle you marked.

You first mark the angle, considering that a positive angle is measured counterclockwise, and a negative angle is measured clockwise. Then you trace the given distance for r in the direction of the angle you marked.

You need only to apply the relations x=rcosθ and y=rsinθ.

The polar coordinate system is the process of describing a point by the distance of the point to the origin and the angle made with the positive x-axis. Take a look at our article for a detailed example.

Final Polar Coordinates Quiz

Question

What is a polar curve?

Show answer

Answer

A polar curve is a curve defined by a relation in terms of polar coordinates \(r\) and \(\theta\).

Show question

Question

How do you identify polar curves?

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Answer

Polar curves are defined by relations in terms of \( r\) and \( \theta\) instead of in terms of \(x\) and \(y\).

Show question

Question

What is symmetry about the pole?

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Answer

Symmetry about the pole is symmetry about the line \( \theta = \frac{3\pi}{4}\).

Show question

Question

What is symmetry about the polar axis?

Show answer

Answer

Symmetry about the pole is symmetry about the line \( \theta = \pi\) (the horizontal axis).

Show question

Question

How do you test for symmetry about the polar axis?

Show answer

Answer

Replace  with  \(r\) with \(-r\) and \( \theta\) with \( \pi-\theta,\) or (equivalently) replace \( \theta\) with \(-\theta\).

Show question

Question

How do you test for symmetry about the pole?

Show answer

Answer

Replace \(r\) with \(-r\) or (equivalently) replace \( \theta\) with \( \pi+\theta\).

Show question

Question

How do you test for symmetry about the vertical axis?

Show answer

Answer

Replace \(r\) with \(-r\) and \( \theta \) with \(-\theta\), or (equivalently) replace \( \theta\) with \( \pi-\theta\).

Show question

Question

Which of the following symbols is the Greek letter theta?

Show answer

Answer

\(\theta\).

Show question

Question

True/False: \(\theta\) can be equal to \(0\).

Show answer

Answer

True.

Show question

Question

In polar coordinates, the ____ is the distance from the point to the origin.

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Answer

radial coordinate.

Show question

Question

Given the point \((r, \theta)\) in polar coordinates, which of the following is exactly the same point?

Show answer

Answer

\( (r,\theta+2\pi) \).

Show question

Question

True/False: The following equations are used to convert from rectangular to polar coordinates.

\[r^2=x^2+y^2\]


\[\tan(\theta)=\dfrac{y}{x}\]

Show answer

Answer

True.

Show question

Question

If \((x,y)\) is in the second or third quadrant, how should you find theta?

Show answer

Answer

\[\theta=\arctan\left(\dfrac{y}{x}\right)+\pi\]

Show question

Question

If \((x, y)\) is in the first quadrant, what is the correct value for theta?

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Answer

\[\theta=\arctan{\left( \dfrac{y}{x}\right)}\]

Show question

Question

If \(x=0\) and \(y\) is positive, what is the value of theta?

Show answer

Answer

\[\theta=-\dfrac{\pi}{2}\]

Show question

Question

If \(x=0\) and \(y\) is negative, what is the value of theta?

Show answer

Answer

\[\theta=-\dfrac{\pi}{2}\]

Show question

Question

In polar coordinates, the angle \(\theta\) is measured ____.

Show answer

Answer

counterclockwise.

Show question

Question

What is a polar function?

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Answer

A polar function, or function written in polar coordinates, is a function that takes in an angle \(\theta \) and returns a distance from the origin.

Show question

Question

What are the steps in converting a function written in polar coordinates to a function written in rectangular coordinates?

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Answer

1. Replace \( \theta \) with expressions in terms of \(x\), \(y\), and \(r\).

2. Replace \(r\) with expressions in terms of \(x\) and \(y\).

3. Simplify.

Show question

Question

What are the steps in converting a function written in rectangular coordinates to a function written in polar coordinates?

Show answer

Answer

1. Replace \(x\) with \( r\cos\theta \) and replace \( y\) with \( r\sin\theta \).

2. Simplify.

Show question

Question

What is the function

\[x^2 + y^2 = 25\]

in polar coordinates?

Show answer

Answer

\(r = 5\) because it is a circle with radius 5 centered at the origin.

Show question

Question

What curve does the equation

\[ r = 5\sec\left(\theta - \frac{\pi}{4}\right) \]

describe?

Show answer

Answer

This equation describes the line with point \( (5, \pi/4)\) closest to the origin.

Show question

Question

What curve is described by a function of the form:

\[ r = a\sin\theta ?\]

Show answer

Answer

A circle of radius \(a\) centered at (0, a).

Show question

Question

What curve is described by a function of the form:

\[ r = a \cos\theta ? \]


Show answer

Answer

A circle of radius \(a\) through the point \( (a, 0)\).

Show question

Question

What curve is described by a function of the form:

\[ r = \frac{b}{\sin\theta - m\cos\theta} ?\]

Show answer

Answer

A line with slope \(m\) through the point \( (0, b)\).

Show question

Question

What curve is described by a function of the form: 

\[r = 2a\cos\theta + 2b\sin\theta?\]


Show answer

Answer

A circle with radius \(\sqrt{a^2 + b^2} \)  through the point \( (a, b)\).

Show question

Question

Is the equation for a circle a function?

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Answer

The equation for a circle can be written as a function in polar coordinates, but not in rectangular coordinates.

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Question

Functions written in polar coordinates always pass the vertical line test.

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Answer

False.

Show question

Question

True/False: The derivative 
\[ f'(\theta) = \frac{\mathrm{d}f}{\mathrm{d}\theta}\]
represents the slope of a line tangent to a polar curve.

Show answer

Answer

False.

Show question

Question

Let 
\[ f(\theta) = 5\theta \]
be an Archimedean spiral. What does its derivative
\[ f'(\theta) = 5\]
describe?

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Answer

How much its radius changes as the angle changes.

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Question

True/False: The line tangent to a polar curve can be vertical.

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Answer

True.

Show question

Question

True/False: The line tangent to a polar curve can be horizontal.

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Answer

True.

Show question

Question

Which of the following is the formula for finding the polar derivative of a curve?

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Answer

\[ \frac{\mathrm{d}y}{\mathrm{d}x} = \frac{f'(\theta)\cdot\sin{\theta}+f(\theta)\cdot\cos{\theta}}{f'(\theta)\cdot\cos{\theta}-f(\theta)\cdot\sin{\theta}}\]

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Question

Which of the following expressions represents the radial speed of an object in motion?

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Answer

\[ v = \frac{\mathrm{d}r}{\mathrm{d}t} \]

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Question

Which of the following expressions represents the angular speed of an object in motion?

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Answer

\[ \omega = \frac{\mathrm{d}\theta}{\mathrm{d}t} \]

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Question

Angular speed is a scalar quantity, while angular velocity is a ____ quantity.

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Answer

vectorial.

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Question

This Greek letter is commonly used to represent angular speed.

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Answer

\(\omega\).

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Question

This letter usually represents the radial coordinate of the polar coordinate system.

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Answer

\( r \).

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Question

This letter usually represents the angular coordinate of the polar coordinate system.

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Answer

\( \theta\).

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Question

This letter usually represents time.

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Answer

\( t \).

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Question

Suppose you use the formula for the derivative of a polar function and obtain infinity. What does this mean?

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Answer

That the line tangent to the polar curve is vertical.

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Question

Suppose you use the formula for the derivative of a polar function and obtain zero. What does this mean?

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Answer

That the line tangent to the polar curve is horizontal.

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Question

Let 
\[ r(t) = t^3 \]
and 
\[ \theta(t) = 5t \]
describe the motion of an object. Which of the following expressions corresponds to its angular speed?

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Answer

\( \omega = 5\).

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Question

How do you draw a point with a negative \(\theta\)?

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Answer

By measuring the angle clockwise from the positive \(x\)-axis.

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Question

True/False: \(r\) can be equal to \(0\).

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Answer

True.

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Question

The point \( (0,0) \) in Cartesian coordinates is known as the origin. How do you name this point on polar coordinates?

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Answer

Pole.

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Question

The pole is obtained by leting \(r=0\). What is the convention for its \( \theta\) value?

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Answer

\(\theta=0\).

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Question

True/False: The following equations are used to convert from rectangular coordinates to polar coordinates.

\[x=r\cos(\theta)\]

\[y=r\sin(\theta)\]

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Answer

False.

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Question

What are polar curves?

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Answer

Polar curves are functions relating \(r\) and \(\theta\) in a polar coordinate system.

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Question

What is the general formula for the area bounded by a polar curve between angles \(\theta_1\) and \(\theta_2\)?

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Answer

\[A = \frac{1}{2}\int_{\theta_1}^{\theta_2} r^2 d\theta\]

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